Defined Benefit Pension Plan and Postretirement Benefits - Net Periodic Benefit Cost and Other Accumulated Comprehensive Income for Pension Plans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Accumulated Other Comprehensive Income Before Tax [Abstract]
Service cost	$ 392	$ 372	$ 237
Interest cost	137	120	102
Recognized actuarial (gains)	(60)	(46)	(55)
Net periodic benefit cost	469	446	284
Unrealized net actuarial (gains), net of tax	(1,150)	(1,413)	(985)
Total amount recognized in net periodic benefit cost and other accumulated comprehensive income (loss)	$ (681)	$ (967)	$ (701)